Experts tackle readers’ garden questions.
Q: Something has happened to our Japanese maple. It is planted on the southwest side of the house. None of the lower branches have evidence of new leaves. All the new growth and leaf buds are on the upper branches. We have had this tree for about 20 years and have never had this problem before. We have not sprayed it with any herbicide or insecticide. We have another red Japanese maple about 50 feet away that seems to be doing fine. And we have neighbors that have Japanese maples that had normal spring growth. Should we cut off the lower branches? They seem very dry and brittle. Is it possible to save this tree?
Master gardener Rachel Tooker: To fully diagnose the reason for the lack of new growth on your Japanese maple, it would be helpful to know a little more, such as the variety of Japanese maple, how frequently the tree is irrigated and by what method, how much sun exposure it receives, the soil type, whether there are any other symptoms on the leaves and branches, and whether there are any signs of insect infestation.
If the tree has been on the south side of your home for 20 years, receiving a significant amount of direct sunlight, it may just be in a slow decline. But here are some thoughts:
Yes, the dead lower branches should be removed. To make sure the branches are indeed dead, scrape off a little of the bark on each branch to see if there is any green tissue underneath. If there is, you can leave the branches in place and see if new shoots or leaves form. If not, you should remove the branches to help keep any potential disease from spreading or insects from entering the dead wood. When pruning, cut back to living tissue, but outside the collar of the branch – this is a small, ridged area where the branch attaches to the trunk. By cutting outside of the branch bark collar, the tree will heal most easily from the cut. In addition, your shears should be sanitized after pruning by dipping them in a 10 percent bleach solution to make sure the disease is not transferred to another plant. Do not dispose of the cuttings in a compost pile.
From your description of the lower branches dying and becoming dry and brittle, it is possible that the tree is receiving too much water and the soil is not draining sufficiently. This may lead to two kinds of conditions: Verticillium wilt and Phytophthora root and crown rot.
Verticillium wilt affects the vascular system of a plant – the network of tissue that transports nutrients, food and water among plant parts. The disease can cause foliage to turn faded green, yellow or brown and wilt in scattered portions of the canopy or on scattered branches. Shoots and branches die, often beginning on one side of the plant, and the entire plant can die if severely infected.
Phytophthora kills the roots and root crown area of infected plants and sometimes spreads upward into the stem. This causes plants to wilt and leaves to discolor, stunt and drop prematurely. Infected mature plants grow slowly and may gradually decline. Twigs and branches die back and the entire plant can be killed. In many, but not all plants, a vertical streak, stain or canker becomes visible on infected trunk wood under the bark. Black or reddish sap may ooze from darkened areas of infected bark.
In both cases, peeling back bark on infected branches may reveal stain streaks in the vascular tissue. The most effective way of preventing these diseases is to provide adequate drainage and practice good water management. Avoid prolonged saturation of the soil or standing water around the base of plants. Irrigate only as much and as often as necessary. Fertilize sparingly with a slow-release fertilizer and continue to prune out any dead wood. The leaves of plants can appear drought stressed, so sometimes home gardeners will respond to these symptoms by adding more water instead of allowing the plant to dry a little between watering.
For more information on Verticillium wilt, go to ipm.ucanr.edu/PMG/GARDEN/PLANTS/DISEASES/vertwilt.html. For more information on Phytophthora, see the UC IPM Pest Note 74133, “Phytophthora Root and Crown Rot in the Garden,” at ipm.ucanr.edu/PMG/PESTNOTES/pn74133.html.
Rachel Tooker is a UC Cooperative Extension master gardener for Sacramento County.
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